The size of an adult’s eye is no more than 2.5 centimeters in diameter, but it is capable of outstanding performance.
In this case, if we have normal sight, we can perceive two points that are distant from each other by only 3 millimeters and 10 meters distant from us!
If we compare the human eye to a camera held by three pairs of hands:
• The 3 pairs of hands would be the six muscles that allows the eye to move from right to left and top to bottom
• The lens of this device would be our cornea (transparent surface membrane of the eye).
• When you press the On/Off button of a camera, the diaphragm opens and closes briefly to allow more or less light: in our eye is the pupil who plays this role!
And what acts as zoom (the focus) is the lens: at rest, the lens is elongated and naturally set to see beyond 60 meters. For near sight, the lens must contract, but its capabilities are limited, there is a distance limit below which we can not see clearly. This distance increases with age because the lens loses elasticity. The minimum distance is 6 cm for children, 15cm at 30,
40 cm at 50 and 1 meter at 70!
Being in focus serves to return the image perceived to the retina, which acts as a memory card of a digital camera: it contains 120 million rod-shaped cells that see in black and white (even if the brightness is low) and 7 million cone-shaped cells, which see in color, but only by day. This is also why it is said that «the night, all cats are gray! » (It no longer perceives color when it is dark).
Received images on the retina are then sent into the visual cortex of the brain via the optic nerve (the equivalent of a USB drive connected to the computer, to download photos). The brain only has to process the information: in this case, it is the brain who reconstructs the relief images from the images received from both eyes simultaneously.
To do so, your computer, must be helped by software!